Archive for March 21st, 2008
烦人的 “Recost for ORDER BY”
Friday, March 21st, 2008
起因是一个SQL走错了索引
SELECT ROWID AS rid
FROM tab_1 s
WHERE s.c_id = :1
ORDER BY s.gmt_r DESC
执行计划如下
——————————————————————————————
| Id | Operation | Name | Rows| Bytes| Cost |
——————————————————————————————
| 0 | SELECT STATEMENT | | 858| 25740| 138K|
|* 1 | TABLE ACCESS BY INDEX ROWID | tab_1 | 858| 25740| 138K|
|* 2 | INDEX FULL SCAN DESCENDING [...]
